A two-part mathematical model has been developed to describe the transport processes in a nucleation chamber designed for condensation of refractory vapors in a microgravity environment. The model solves the transient diffusion equations for temperature and concentration fields in cylindrical coordinates using finite differences and the alternating direction implicit method. Vapor supersaturation ratios are then computed from the evolving concentration profiles thus permitting one to estimate the conditions at the location in the chamber where nucleation is observed in experiments.